The invention relates to an image receiving material for dye diffusion thermal transfer providing a thermal dye transfer as well as to a method for the production of such image receiving material. 2. Brief Description of the Background of the Invention
Including Prior Art
The system of thermal dye transfer or dye diffusion thermal transfer, abbreviated "D2T2", developed in recent years, allows the reproduction of an electronically generated image in the form of a hard copy.
The principle of the thermal dye transfer comprises that the digital image is prepared with respect to the base colors: cyan, magenta, yellow, and black, and is transformed into corresponding electrical signals. These signals are transformed to a thermal printer and are converted into thermal energy. Based on thermal heating effect, the dye sublimes from the donor layer of an ink ribbon or an inked sheet, contacting the receiving material, and diffuses into the receiving layer.
A receiving material for thermal dye transfer comprises in general a support substrate with a receiving layer placed onto the front side of the support substrate. Frequently, other layers are also applied to the front side of the support substrate in addition to the receiving layer. Such layers include, for example, a barrier layer, a separating layer, an adhesion layer, and a protective layer.
Support substrates can be plastic foils such as, for example, polyester foil or a resin-coated paper.
The receiving layer comprises in general a thermoplastic resin as a main component, where the thermoplastic resin exhibits an affinity to the dye of the inked ribbon. Such thermoplastic resins include linear polyesters, for example, polyethylene terephthalate, polybutylene terephthalate, or acrylic resins, for example, polymethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, etc. In addition, polystyrene, polycarbonate, polyvinyl pyrrolidone, ethyl cellulose, polysulphones, or other plastic materials can be employed as dye accepting resins.
The following requirements are imposed on the receiving material for the thermotransfer.
A surface smoothness is required.
A stability to deformation by heat/pressure is required.
Print stability, i.e., a uniform print appearance (no blurs or mat spots) is required.
A stability to light is required and no tendency to yellowing can be permitted.
A good dye solubility is required.
A good resistance to scratching and abrasion is required.
Anti-blocking properties are required and sticking together of receiving material is not permissible.
In order to meet these requirements, several different paths have been taken.
It is known from the U.S. Pat. No. 4,748,150 and from the U.S. Pat. No. 4,774,224 to apply a receiving layer made of polycarbonate onto a polyethylene-coated base paper. In addition, a subbing layer is applied between the support substrate and the receiving layer. The subbing layer, comprising a vinylidene chloride copolymer, is furnished to improve the adhesion of the receiving layer on the support substrate material.
It is a disadvantage of this receiving sheet that the polycarbonate, employed according to U.S. Pat. Nos. 4,748,150 and 4,774,224 tends very strongly to yellow and that this influences negatively the transferred picture in the course of time. A further disadvantage is associated with the situation that both layers (subbing and receiving layer) are applied from an organic solvent phase, which raises problems and questions relative to health and safety issues.
The problem of the stability against light impingement was intended to be solved according to the U.S. Pat. No. 4,775,657 by applying a protective layer of polyester or polyurethane onto a receiving layer formed of polycarbonate. It is a disadvantage of this method that the print stability of the receiving sheet, produced in this manner, is relatively low and that this method is associated with the application of the layers from organic solvent phases.
The European Patent Application EP-0,261,970 describes a good heat resistance of the receiving sheet and a good anti-blocking properties of the receiving layer. For this purpose, a single layer is recommended, which comprises in addition to a linear saturated polyester as binder also a silane copolymer coupled with silica as a separating agent.
The Japanese Printed Patent document JP 0,270,487 claims a receiving layer comprising vinyl chloride/vinyl acetate copolymer as binder, where the receiving layer is to assure a high density of the transferred picture image and wherein additionally good anti-blocking properties are to be achieved based on the incorporation of silicone oil into this layer. It is a disadvantage of this receiving material that there is a poor line sharpness of the transferred image and that the layer is applied from a solvent phase.